cpufreq: intel_pstate: Remove EPB-related code

The intel_pstate driver does not enable HWP mode when CPUID.06H:EAX[10]
is not set, indicating that EPP (Energy Performance Preference) is not
supported by the hardware.

When EPP is unavailable, the system falls back to using EPB (Energy
Performance Bias) if the feature is supported. However, since the
intel_pstate driver will not enable HWP in this scenario, any EPB-related
code becomes unreachable and irrelevant. Remove the EPB handling code
paths simplifying the driver logic and reducing code size.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20250904000608.260817-1-srinivas.pandruvada@linux.intel.com
[ rjw: Subject adjustment ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: spandruvada

drivers/cpufreq/intel_pstate.c

@@ -620,24 +620,9 @@ static int min_perf_pct_min(void)
 		(cpu->pstate.min_pstate * 100 / turbo_pstate) : 0;
 }
 
-static s16 intel_pstate_get_epb(struct cpudata *cpu_data)
-{
-	u64 epb;
-	int ret;
-
-	if (!boot_cpu_has(X86_FEATURE_EPB))
-		return -ENXIO;
-
-	ret = rdmsrq_on_cpu(cpu_data->cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb);
-	if (ret)
-		return (s16)ret;
-
-	return (s16)(epb & 0x0f);
-}
-
 static s16 intel_pstate_get_epp(struct cpudata *cpu_data, u64 hwp_req_data)
 {
-	s16 epp;
+	s16 epp = -EOPNOTSUPP;
 
 	if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
 		/*
@@ -651,34 +636,13 @@ static s16 intel_pstate_get_epp(struct cpudata *cpu_data, u64 hwp_req_data)
 				return epp;
 		}
 		epp = (hwp_req_data >> 24) & 0xff;
-	} else {
-		/* When there is no EPP present, HWP uses EPB settings */
-		epp = intel_pstate_get_epb(cpu_data);
 	}
 
 	return epp;
 }
 
-static int intel_pstate_set_epb(int cpu, s16 pref)
-{
-	u64 epb;
-	int ret;
-
-	if (!boot_cpu_has(X86_FEATURE_EPB))
-		return -ENXIO;
-
-	ret = rdmsrq_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb);
-	if (ret)
-		return ret;
-
-	epb = (epb & ~0x0f) | pref;
-	wrmsrq_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, epb);
-
-	return 0;
-}
-
 /*
- * EPP/EPB display strings corresponding to EPP index in the
+ * EPP display strings corresponding to EPP index in the
  * energy_perf_strings[]
  *	index		String
  *-------------------------------------
@@ -782,7 +746,7 @@ static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
 					      u32 raw_epp)
 {
 	int epp = -EINVAL;
-	int ret;
+	int ret = -EOPNOTSUPP;
 
 	if (!pref_index)
 		epp = cpu_data->epp_default;
@@ -802,10 +766,6 @@ static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
 			return -EBUSY;
 
 		ret = intel_pstate_set_epp(cpu_data, epp);
-	} else {
-		if (epp == -EINVAL)
-			epp = (pref_index - 1) << 2;
-		ret = intel_pstate_set_epb(cpu_data->cpu, epp);
 	}
 
 	return ret;
@@ -1337,9 +1297,8 @@ static void intel_pstate_hwp_set(unsigned int cpu)
 	if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
 		value &= ~GENMASK_ULL(31, 24);
 		value |= (u64)epp << 24;
-	} else {
-		intel_pstate_set_epb(cpu, epp);
 	}
+
 skip_epp:
 	WRITE_ONCE(cpu_data->hwp_req_cached, value);
 	wrmsrq_on_cpu(cpu, MSR_HWP_REQUEST, value);